IP Address Conflict Message Help!

I keep loosing my wireless connection every now and then since yesterday. It happened on all four of my computers. It started after I changed my wireless security from wpa2 personal (aes) to wpa personal. My router is Linksys wrt160n version 3. I have updated to the latest firmware 3.0.3. I have tried to power cycle it and even reseting the router to factory defaults, but the ip conflict message persisted. If you have a solution please post. Thanks!

I have looked at all the computer currently connected to the router and all of them is using an unique ip address. The computers just disconnect and connect again occassionally and sometimes it said ip conflict.